1. Field of the Invention
The present invention relates to a method for transferring nanostructures into a substrate, in which method nanomaterials are used as a shadow mask for applying a coating.
Furthermore, the invention relates to a surface comprising transferred nanostructures, which surface has been produced according to a method according to the invention, a membrane, an electrode device or a biosensor which have such a surface, and also a device having a surface, membrane, electrode device and/or biosensor according to the invention.
2. Related Prior Art
The production of nanostructures having dimensions of less than 100 nm (electron beam lithography, focused ion beam lithography, UV lithography, X-ray lithography) requires very expensive lithography apparatuses. The economic and reliable production of components having such nanostructures (e.g. filter membranes having monodisperse pore distribution having dimensions of 20 nm to approximately 500 nm) therefore requires new production technologies. If these structures are intended to be produced periodically and over relatively large areas, an appropriate alternative to conventional lithography methods, such as photolithography, electron beam lithography or nanoimprint lithography, for example, is the method of particle lithography; Fischer and Zingsheim, J. Vac. Sci. Technol., 19(4), November-December 1981.
Various methods in which nanostructures are transferred to substrates by means of particle lithography are known in the prior art.
JP 11066654 describes a method in which, in a first step, nanomaterials are applied to a substrate coated with an adhesive layer in order to bind the nanomaterials. In a second step, nanostructures are transferred into the substrate by etching, and in a further etching step the nanomaterials and the adhesive layer are removed.
The abovementioned publication “Submicroscopic pattern replication with visible light” (Fischer and Zingsheim, 1981) describes a method for producing a nanostructured exposure mask in which a glass substrate is decorated with nanomaterials in a first step, a coating with a metal is applied in a second step, and the nanomaterials are removed in a third step.
The publication “Nanosphere lithography: A materials general fabrication process for periodic particle array surfaces” (Hulteen and Van Duyne, 1995, J. Vasc. Sci. Technol. A 13(3)) describes a method for producing periodic particle structures on a substrate. In this case, the substrate is decorated with a one- or two-layered periodic arrangement of nanomaterials in a first step, a coating is applied in a second step, and the nanomaterials are removed from the surface in a third step.
The known methods all have different disadvantages, however. Thus, in particular a problem with regard to the removal of the nanomaterials used as a mask arises in the known methods for particle lithography.
By way of example, it is known from the abovementioned publications by Fischer and Zingsheim as well as by Hulteen and Van Duyne to remove the nanomaterials from the substrate by means of irradiation with ultrasound. What is disadvantageous in this case is that when the ultrasonic power is set too low, particles adhere on the substrate and are only partly removed. If the power is too high, by contrast, not only the particles but also the applied coating is partly removed. On account of the process-inherent unequal extent of ultrasonic intensities, it is thus only possible to implement these methods with a low number of defects on areas on the submillimetre scale.
Furthermore, JP 11066654 mentioned above describes removing the nanomaterials by means of plasma etching. What is disadvantageous in this case is that the substrate surface itself is also altered by the etching process.
A further method for removing nanomaterials from a coated surface is described in the abovementioned publication by Hulteen and Van Duyne. This method involves lifting off the nanomaterials with adhesive film from the coated substrate.
This method also has disadvantages. A defect-free lift-off of the nanomaterials is possible only on extremely small areas of less than 1 mm2. Furthermore, there is also the risk here of the underlying coating being damaged as a result of detachment from the substrate.
A further problem of the known methods is the restriction with regard to the lower limit of the resolution. Thus, only nanostructures which have a significantly larger extent than the thickness of the applied coating can be transferred into the substrate by the known methods. The reason for this is that during the application of the coating, smaller nanomaterials would be completely or substantially embedded into the coating, and would thereupon no longer be removable.